Offshore Mooring Catenary Tension & Touchdown Calculator
Calculate mooring line top tension at fairlead, catenary curve parameter, anchor touchdown point, and horizontal seabed pull per API RP 2SK & DNV-OS-E301.
Mooring Water Depth & Line Specs
Applied Environmental Horizontal Load
Catenary Line Tension & Profile
| Catenary Characteristic Parameter (a): | -- m |
| Critical Suspended Length (S_crit): | -- m |
| Grounded Line on Seabed (L_ground): | -- m |
| Vertical Reaction at Fairlead (V): | -- kN |
| Fairlead Declination Angle (φ): | -- deg |
| Touchdown Distance from Fairlead (X_td): | -- m |
| Total Anchor Horizontal Reach (X_anchor): | -- m |
Recommended Tools & Equipment
Tested hardware and components for high reliability
Frequently Asked Questions
Why must a conventional drag-embedment mooring line maintain tangential seabed touchdown?
Conventional drag-embedment fluke anchors (such as Stevpris, Danforth, or Bruce anchors) derive their high holding capacity solely from horizontal resistance within marine soil. Any upward vertical load at the anchor shackle flips or dislodges the fluke, leading to catastrophic mooring breakout and vessel drift. API RP 2SK requires sufficient line length so that a grounded length of heavy chain remains on the seabed even under maximum design storm offsets.
What is the relationship between catenary top tension and fairlead depth?
For a freely hanging catenary touching bottom horizontally, the top tension is related by T_top = H + w * h, where H is horizontal tension, w is submerged line weight per unit length, and h is water depth. This demonstrates that deepwater catenary systems experience massive deadweight vertical tensions simply from supporting the heavy steel chain suspended in the water column.
How does API RP 2SK define safety factors for offshore mooring lines?
Under API RP 2SK, the factor of safety (MBL / Tension, where MBL is Minimum Breaking Load) must be at least 1.67 for quasi-static design under intact storm conditions, 1.25 for damaged conditions (one line broken), and 2.0 for permanent production facilities in benign or normal operating environments.